This is a genuine US M1917 helmet. Helmet is in untouched condition, exactly as it came to us as.
The US M1917 started out as a American made copy of the British MkI helmet. It differed only slightly, namely the methods of attaching the chinstrap bales (British MkI's used split pins, American M1917's have rivets) and the seam of the rim attached to the edge of the helmet. British MkI's have rims that overlap, US M1917's have it flush. Additionally, US made M1917 helmets have a "Z" prefix on the steel lot code, British ones do not.
Lot code on the shell is difficult to read, but it appears to be ZD74.
Finish on shell has some rust and patina. There is some rust and scuffs on the shell consistent with a helmet that is over 100 years old. The liner is missing, as is the chinstrap. It is effectively just a shell, but would look great on a shelf.
While we do not recommend wearing it, it would look great on display. Perfect for WW1 collectors or for restoration.